In the last fifty years a large industry has evolved providing synthetic hydrocarbon fluids such as polyalpha olefin (PAO) fluids for a host of lubricant applications. The uniquely superior properties of SHF, particularly PAO fluids, for automotive engine oil lubricant applications have made them a common item of commerce throughout the industrialized world. Polyalphaolefins have traditionally been the synthetic fluids of choice when selecting a SHF for engine lubricant applications for they have offered the best combination of viscosity-temperature relationship with good viscosity index (VI), very low pour point, low viscosity at low temperature, low volatility and excellent thermal stability. Also, alpha-olefins are readily available and readily polymerizable thermally or, most preferably, cationically using Lewis acid catalyst. However, PAO does exhibit certain limitations in that significant branching occurs during polymerization which results in extremely good but less than optimum properties.
It has been established that structural linearity in the lubricant molecule is a preferred structure for optimizing properties. However, structural linearity also promotes solidification of the liquid lubricant at unacceptably high temperatures, i.e., high pour point. Resolving this dilemma has been a major challenge to investigators in the field.
While the degree of branching that occurs in conventional PAO may compromise the potential performance of PAO as a lubricant, a PAO of near-linear structure, HVI-PAO, that provides excellent VI at low pour point has been discovered and reported in U.S. Pat. Nos. 4,827,064 and 4,827,073. HVI-PAO is produced by oligomerization of alpha-olefin with carbon monoxide reduced chromium oxide catalyst on silica support. These PAO oligomers have a methyl-to-methylene branch ratio of less than 0.19 and cover a wide range of viscosities.
Individual trialkyl methane compound are known in the art in pure form including trioctylmethane and tridecylmethane as reported in Research Project 42 report of the American Petroleum Institute Division of Science and Technology, 1940-1967. However, they have melting points (&gt;7.degree. F.) and are therefore unsuitable for lubricant applications.
An object of the present invention is the identification of tri-n-alkylmethane lubricants which have low pour points, good thermal stability, low viscosity, high VI and low volatility.
A further objective of the present invention is to provide a process for the preparation of mixed tri-n-alkyl methane lubricants having the foregoing properties.